I’ve worked with several different pond liner products over the years and here’s my take on them. You’re going to see a ton of conflicting advice but do check out the bottom line from my experiences.
Here is a look at some of the more popular that you’ll read about.
This is extremely durable, very puncture resistant (good if you’re using large rocks as islands) and flexible. It is the gold standard in pond liner construction.
Note that flexibility is good for ponds with lots of corners or ledges or curves.
Polyethylene Pond Liner
This is the cheapest alternative but it degrades rather quickly in sunlight, is stiff to work with not overly puncture resistant.
It is roughly half the cost of the others though and if you have a huge pond with a sandy bottom (and can bury the edges of the poly so they don’t show, this might be your cheapest alternative)
It’s not a great product for a small pond as the guarantees are not all that long.
Good polypropylene is more durable than epdm and likely more puncture resistant but it is a heck of a thing to work with (like polyethylene) because it is stiff and not very flexible.
Really small water gardens with ledges and planting holes should stay away from this material because of its stiffness. It is slightly more expensive than epdm. Its strength is a bonus on larger ponds.
Swimming Pool Liners
I do get asked about using an old swimming pool liner for ponds. The cautions are the same as above; it depends on what those liners were made of whether it will be fish-safe. I also note that most old swimming pool liners have sun degradation around the upper edges are are “stiff”; these two characteristics will make it a problem for both long term use of the liner and for installation.
So the answer is the same – you can use an old pool liner but you take your chances. Is it worth the savings? Only you can answer that.
As a last note, good underlay will save you time and money in the long run. I know that there is advice out there on using newspapers and old carpets (I’ve used both) but they can be a pain to use. If you’ve ever tried laying old newspapers on the vertical side wall of a pond, you’ll have some sense of what I mean.
Carpets and newspaper can be used on the bottom of ponds if you have the time to mess around with laying them smoothly and evenly but for my money, I’d still use the proper pond underlay over top of them to protect the liner along the edges of the pond.
In summary, you can work with the pond material of your choice but the best all-round choice is EPDM